Composite wire



Patented Jan. 29, 1935 UNITED STATES PATENT OFFICE COMPOSITE WIRE Delaware No Drawing.

Application June 1, 1928,

Serial N 0. 282,273

6 Claims.

sealed envelopes. The composite conductor of this invention may also be employed as a conductor for spark plugs, mercury gauges or valves.

It is further very easily coated with electron emitting substances; preferably oxides or carbonates, and when so coated has very great advantages as a filament for radio vacuum tubes.

It is the object of this invention to provide a composite conductor comprising a core of metallic materials having a low coeflicient of expansion and a sheath having a marked tendency to absorb or combine with gases such as hydrogen or other reducing or fluxing gases.

In former times the lamp art was confined to the use of platinum wires for lead-in conductors for the reason that platinum had a coeflicient of expansion very close to that of ordinary glass and also because the glass in its fused condition would wet the platinum wire and on cooling adhered intimately to the wire, thus making a hermetical seal. The cost of platinum was so great, however, that efforts were constantly being made to produce a serviceable substitute therefor. Early attempts resulted in the production of a wire composed of nickel iron or nickel steel in varying proportion. By varying the relative proportions of the nickel and iron, this wire could be made so as to have a co-efiicient of expansion sufiiciently close to that of any ordinary glass, so that it seemed to be admirably adapted for the purpose. One defect, however, rendered it unsuitable. The iron in the wire had a tendency to oxidize at the temperatures involved in the sealing-in operation and a coating of oxide thus forming on the surface prevented the fused glass from wetting and adhering thereto. This made it diflicult to maintain a good vacuum where such wires were sealed through the glass.

It was then proposed to sheathe the nickel iron core with copper for the fused glass will adhere to copper very intimately although in the case of a pure copper wire, the coefiicient of expansion is so different from that of glass that it had a tendency to pull away from the glass" on cooling and thus permit leakage. The nickel iron core with the copper sheath however, was found very serviceable and made excellent seals with the glass particularly when the copper was coated with a film of borate.

I have discovered however, that a core consisting preferably of nickel steel or nickel chrome steel (the nickel and steel or the nickel and chromium and steel being in such relative proportions as to produce a low expansion core) may be clad or sheathed with nickel and so treated in 5 hydrogen at elevated temperatures that the composite wire so formed will be excellently adapted for the purpose of sealing through glass and also for various other purposes above mentioned. The wire of this invention, for instance, is ex- 10 cellently suited for coating with electron emitting oxides such as those of barium and strontium and when so coated forms a very efficient filament material for radio vacuum tubes.

I may, for example, form the core of my composite conductor of a nickel chrome steel in which the nickel constitutes approximately 40% to 42% and the chromium 0.10% to 5.0%. This forms a core having a verylow coefiicient of expansion. A greater or less proportion of nickel may be used in order to adapt the conductor for special purposes, but in either case the coefiicient of expansion will be higher than if the proportion be that above stated. I may also compose the sheath of the conductor either of pure nickel or of a nickel alloyed with another metal in comparatively small proportions, such as tantalum or like metal having a marked tendency to absorb or combine with hydrogen. By these means, I can produce a composite conductor having a coefficient of expansion equal to that of the copper clad wire but having a higher resistance and melting point and saturated with a large volume of hydrogen. The sheath of the wire may even be covered with a thin film of hydride. At the temperatures involved in coating the conductor or in sealing through glass, the hydrogen released from the wire or from the hydride film acts as a flux beneficially influencing the coating of the wire in the one case and furthering the wetting of the wire by the glass in the other case so as to produce an intimate hermetical seal between the two. Furthermore, the high electrical resistance of the composite conductor as a whole is of very great advantage where the conductor is used as a coated filament for radio tubes in that it serves to attain and maintain the temperature necessary for most efiicient electron emission.

This adhesion between the conductors and the embedding or coating material is due in some degree also to the low coefiicient of expansion when the core contains the proportion of nickel above mentioned, it has a coefllcient of expansion much lower than that of platinum. But even when the nickel is in such proportion (more than ,50%) that the coemcient of expansion is higher than that of platinum, it is sufliciently low to produce beneficial results for the reason that the sheath material serves as a cushion between the core and the embedding or coating materials and will adhere to both throughout temperature ranges of considerable magnitude.

In making my composite conductors, I employ a central core of the material. the nickel being in such proportion as to have the desired coefllcient of expansion. The rod or bar forming this core is first wrapped in a thin sheet of suitable brazing material. The core with its wrapping is then inserted into a tube of either pure nickel or a nickel alloy as above mentioned.

The proportions of the core material in relation to the tube or sheath material may vary in accordance with the purpose for which the flnished wire is to be used. Thus, for a lead-in wire for an incandescent lamp or radio tube, I may employ in the first stage of manufacture as a core, a rod of such diameter and a tube or sheath having walls of such thickness that when the composite rod so formed is drawn down to wire, the sheath will form about 25% to 30% of the total amount of material composing such wire. On the 1 other hand, if the wire is to be used as a conductor for spark plugs, I may so arrange the quantities of the materialsrelatively to each other that the sheath material comprises 10% to 15% of the whole.

I may for example, employ a rod or billet of the low expansion metal of 0.725" diameter, carefully polish its surface and slip over it or wrap around it a thin layer of brass, silver or copper and then slip over that the exterior sheath or tubing of nickel or nickel alloy of .750" inside diameter by #17 Stubbs gauge. The three elements are then swaged sufllciently to shrink the exterior sleeve tightly on to the inner core.

The bars are then placed in a vertical position in a furnace having an atmosphere of hydrogen or other suitable inert or reducing gas. In the furnace the bar is held on a suitable support of metal in such manner that the upper portion is within a region of temperature sufllcient to melt the brazing material while the lower portion is maintained in a comparatively cool state by keeping it out of the fusing temperature and by the cooling effect of the support. In this way the brazing material at the upper portion of the rod is caused to fiow about the core but prevented from escaping at the bottom. By suitably adjusting the bar in the furnace the brazing material may be fused ultimately along the whole length of the rod and a uniform joint thus formed between the sheath and the core.

By another method I may unite the exterior sheath to the inner core by slipping the sheath over the core and then mechanically working the two by hot rolling or swaging it without the use of intermediate brazing material, thus welding the sheath on to the inner core through the combined action of heat and pressure.

The initial form of my composite product is preferably a billet or ingot about two to three feet in length. From this by swaging and drawing by well known methods I produce rods or wires which may be rolled further in ribbons if desired. This final product is finally subjected to a high temperature treatment in pure hydrogen so that it becomes thoroughly annealed, is free of oxygen and is saturated with hydrogen gas. This hydrogen treatment may be carried to the extent of forming a thin film of hydride on the surface of the finished composite wire. In any case the hydrogen acts very advantageously where the wire is sealed through glass in that it acts as a flux causing the glass to wet" the wire and adhere to it and reduces oxidation. It is also of advantage where it is desired to cause coatings of oxides or other materials to adhere to the nickel in that it has a reducing action upon the oxide or carbonate coatings when the latter are heated.

I am aware that wires having a core of ferrous material and an exterior covering of copper, silver or gold are old and that they have disadvantages which my invention aims to overcome. Such disadvantages as may be enumerated are:- That they will amalgamate with the mercury in mercury devices which the, nickel coated wire of this invention does not do. Also metals of the copper group have a relatively low vaporization point in a vacuum and have a relatively high conductivity. In addition, such wires when used as coated filaments, are not successful largely because the copper appears to have a detrimental effect upon or tends to poison the emission. By properly correlating the constituents of my composite conductors, I am able to procure a. wire of high resistance with consequently higher electronic emission in the case of coated filaments and to provide lead-in wires capable of being sealed through refractory glasses and vitreous. materials even where unusually wide ranges of temperatures are employed. This is a distinct advance over the present day lead-in wires which can be used only for sealing through ordinary glass in a temperature range of about 300 C. to room temperature.

Many changes and variations may be made in my invention without departing from the spirit thereof and I desire to include all such changes and variations within the scope of my claims.

I claim:-

1. A composite conductor suitable for lead-in wires for sealing into glass, said conductor comprising a core of low expansion metal; and an external metallic sheath which comprises tantalum and which has a hydrogenized coating positioned to come into direct contact with the glass.

2. In combination, a metallic lead-in wire made up of a metallic core having a low coeflicient of expansion and a metallic sheath comprising nickel having hydrogen incorporated therewith adapting it to be wetted by molten glass; and a body of glass into which said wire is sealed with its hydrogenized nickel sheath in contact with the glass.

3. A composite metallic wire, consisting of a core of nickel alloy and a metallic sheath of nickel-containing metal, said sheath being saturated with hydrogen.

4. A composite metallic wire, consisting of a core of nickel alloy and a metallic sheath of nickel-containing metal, said sheath being saturated with hydrogen to the extent of forming a hydride on the surface of the wire.

5. The product of claim 3, in which a metal having a marked afiinity for hydrogen is present in the sheath.

6. The product of claim 3, in which the wire is coated with electron-emitting oxides.

' CLEMENS A. LAISE. 

